This invention relates to radio frequency communications and more particularly to apparatus and methods for identifying and communicating with radio frequency devices based on location.
Safe aircraft operation depends in large part on the ability to successfully communicate with different radio devices on or above the earth's surface. In general, radio devices may include devices such as transmitters, receivers, transceivers, transponders, or the like that may be used for navigation, communication, or other purposes. A radio device may be designed to transmit and receive signals over one or more selected communication frequencies. As such, transmitters and receivers must normally be located within a certain distance of one another to communicate effectively. This distance may depend on the transmitting frequency, transmitting power, antenna type and orientation, receiving sensitivity, and relative elevations of transmitter and receiver, among other factors.
For example, VHF Omni-directional Range (VOR) is one type of radio navigation system used by aircraft. An aircraft operating at a given altitude may be able to detect a signal from a VOR transmitter, also located at some altitude, within some radius of the VOR transmitter. This radius may increase as the aircraft's altitude above the VOR transmitter increases. For example, an aircraft radio operating at 5000 feet above a VOR transmitter may be able to detect the VOR signal within a radius of about 30 miles. If the altitude of the aircraft radio is increased to 10,000 feet, this radius may increase to about 50 miles.
Similarly, communication equipment such as air traffic control, approach control, tower and ground voice communication equipment may be operable some distance from an airport facility and may depend on an aircraft's elevation relative to the facility. The range may be affected by mountains or other obstructions, which may interfere with higher frequency communications, and by factors such as transmitter power, which may vary depending on the time of time of the day (e.g., the transmitting power may be reduced at night).
Often, a pilot or radio operator will attempt to communicate with a radio device but will be unsuccessful because the device is out of range. This may cause the pilot to spend valuable time assessing the situation. For example, the pilot may spend time verifying that the correct radio frequency is selected on the aircraft radio, checking the aircraft position (including altitude) relative to the radio device, or checking for obstacles such as mountains that may be interfering with communication. In some cases, a pilot may attempt to communicate over an incorrect frequency. This may consume valuable pilot time and interfere with other pilots trying to utilize the same frequency. This may also create safety risks or cause substantial embarrassment to the pilot. It is not uncommon to hear attempts to communicate over incorrect frequencies, especially in areas of uncontrolled airports.
Currently, various navigation computers allow an operator to program a flight plan or flight route into the navigation computer. These navigation computers are typically coupled to a GPS receiver or other position-locating device. If the pilot desires, the navigation computer may be programmed to automatically select navigation aids as waypoints are passed while flying. For example, the navigation computer may be programmed to switch from a GPS receiver to an Instrument Landing System (ILS) receiver when an aircraft reaches an ILS path. This operation, however, typically requires the pilot to program the flight route into the navigation computer.
Current GPS receivers may also be configured to display the current location of an aircraft or other vehicle moving across a map. In aviation applications, these maps may be configured to display navigation or voice communication frequencies associated with various waypoints that are programmed into the GPS as part of a flight route. For example, a GPS receiver may be configured to display communication frequencies associated with a destination airport when the airport appears on the map or when the aircraft approaches the airport. Like the navigation computers previously described, these functions typically require that the pilot program the GPS receiver.
GPS receivers utilized with aviation applications often have a nearest airport function where a pilot can quickly locate the nearest airport, along with that airport's important radio frequencies. This information is typically stored in a database in the GPS. This function is quite useful in emergencies or in situations where the aircraft's passengers need a bathroom break. Unfortunately, while the airport radio frequencies are made available to the pilot, communications with the airport may not be possible because of distance, obstructions, and/or altitudes of the aircraft and airport.
Automobile radios often include favorite station memories which may be programmed by an operator such that a particular favorite station may be selected by simply pushing a button. These radios often include several sets of such memories, allowing an operation to select a set and thereby select the stations associated with that set. Drivers who commute to different cities often program these sets to include favorite stations associated with each city.
In view of the foregoing, what is needed is an apparatus and method to automatically present a list of radio devices within range, or substantially within range, of a vehicle, without requiring substantial programming by an operator. Ideally, such an apparatus and method would save time and reduce the chance that an operator would attempt to communicate over an incorrect frequency. Further needed are apparatus and methods to effectively present a list of such radio devices to an operator. As will be seen, the invention provides such solutions in an elegant manner.